In a two-stroke internal combustion engine, there is a period during which both the intake port and the exhaust port are open. Therefore, the phenomenon occurs in which the fuel supplied in the cylinders is exhausted into the exhaust port in the unburnt state, i.e., so-called "blowby" occurs. When blowby occurs, there are the problems of deterioration of the rate of fuel consumption, an increase in the emission of toxic exhaust, etc., so it is necessary to reduce such blowby. Toward this end, it is possible to provide a fuel injection valve for directly spraying fuel in the cylinder and to delay the fuel injection timing of the fuel injection valve so as to reduce the blowby.
However, in the case of direct injection of fuel into a cylinder, it is not possible to sufficiently disperse and atomize the fuel by the flow of intake air as in the case of injecting fuel into an intake port. Further, if the fuel injection timing is delayed, as the time from the injection of the fuel to the ignition becomes shorter, it is not possible to vaporize the fuel sufficiently. Therefore, there is the problem that good ignition and combustion cannot be obtained.
As a countermeasure, Japanese National Publication (Tokuhyo) No. 63-50032 discloses a two-stroke internal combustion engine which has an intake port and exhaust port on the inner peripheral side surface of the cylinder to enable direct injection of fuel in the cylinder, said two-stroke internal combustion engine injecting into the cylinder at least 80 percent of the amount of fuel injection before the closing of the exhaust port during high load engine operation so as to improve the dispersion and atomization of fuel in high load engine operation.
However, such a two-stroke internal combustion engine tries to improve the dispersion and atomization of fuel just by lengthening the time from the injection of fuel in the cylinder to its ignition, so the dispersion of the fuel and the atomization and vaporization of the fuel are still insufficient and therefore it is not possible to obtain excellent ignition and combustion.